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TEXTBOOK OF ZOOLOGY 



tract ends blindly in many bracliiopods. The entire tube is lined 

 internally with ciliated epithelium. A segmented, true coelom is 

 present, but the septa are a little bit difficult to distinguish. Exten- 

 sions of the coelom enter the arms and mantle of this type of animal. 

 About two pairs of nephridia are connected with the coelom and 

 serve in excretion. The coelomic cavities produce the gonads also. 

 The sexes are distinctly separate and mature germ cells are dis- 

 charged into the coelom, thence to nephridia and outside. Fertili- 

 zation takes place in the water, and a free-swimming, ciliated larva 

 hatches from the egg. 



Digestive gland 

 Stomach 

 Heart 



Adductor muscle 

 I 



^ophophore 

 / i Dorsal valve 



' Dorsal mantle 



Intestine 

 Nephridium 



Muscle 



Mouth 



Pig. 95. — Diagram of a sagittal section of a brachiopod to show internal organs. 

 (From Hegner, College Zoology, published by The Macmillan Company.) 



Magellania flavescens and M. lenticularis are commonly studied 

 forms. They are entirely marine and represent an old line of ani- 

 mals. There are relatively few modern forms in existence. The 

 group is of little economic significance. 



TROCHELMINTHES 



The rotifers (Rotifera) are common examples of this group known 

 as the Trochelminthes (trok el mm'thez — wheel worm). In early 

 times they were called "wheel animalcules." There is very little 

 difference between the trochophore larva of this group and the 

 adult animal. Gastrotricha constitutes another small division of 

 this group but will not be discussed in detail here. 



